1. Field of the Invention
The invention relates to molecular chemical compounds for optical devices, which have structures allowing electron displacement and capable of emitting photoluminescent radiation, and photoluminescence quenching devices (display devices) employing the same.
2. Description of the Related Art
Chemical compounds possessing the property of absorbing high-energy radiation (UV radiation, X-ray radiation, cathode radiation, etc.) and transforming the same into longer-wave, normally visible, radiation are referred to as luminophores. The process is called luminescence. Luminescence processes can be classified as to the type of energy supply. For example, in photoluminescence, an electron is promoted to a higher energy level by optical excitation (irradiation), whereas, in electroluminescence, an electron is promoted to a higher energy level by applying an electric field.
Photoluminescence quenching devices (PQDs) are known as a display device applying photoluminescence technology used under outdoor conditions, e.g., in strong sunlight. The photoluminescence quenching devices use exterior light to generate photoluminescent light which can be modulated by means of an applied voltage. These display devices can be operated in an auto-emissive mode which can be utilized under conditions where exterior light is sparse or absent.
The basic principle of the photoluminescence quenching device is well known. It involves a mechanism wherein splitting of the excited state permits controlling the intensity of emitted light. Such splitting produces charge carriers which are removed via the contacts. Hence, the mechanism of the photoluminescence quenching device proceeds inversely to that of an organic light-emitting diode (OLED) wherein charge carriers undergo recombination with emission of light.
Conjugated polymers selected from materials having a poly(phenylenevinylene) (PPV) or polyfluorene (PFO) basic structure are presently used as materials in PQDs. However, these materials have been developed for use in polymer organic light-emitting diodes (PLEDS) and show fluorescence quenching of more than 70% only at relatively high electric fields of 2.5×108 V/m when used in PQD devices.
Donor-acceptor structures having non-linear optical properties were disclosed. Chiral materials for non-linear optical uses were disclosed by Stewart et al. in U.S. Pat. No. 6,288,206B1 and polymers for non-linear optical uses were disclosed by Sasaki in U.S. Pat. No. 5,745,629A. However, emission of photoluminescent radiation is of secondary importance in these patents because the field dependence of the absorption and, in particular, that of the refractive index are to be utilized with priority. The compounds which exhibit very strong donor-acceptor interactions even in the ground state of the material are not appropriate for photoluminescence quenching devices because these compounds are non-emissive due to high polarity.